Malformations of the gill filaments of the ruffe Gymnocephalus cernuus (L.) (Pisces) caused by echinostomatid metacercariae

Abstract

In parasite surveys of fishes from Lake Balaton and its tributaries in Hungary, infections with metacercariae of a species of the digenean genus Echinochasmus (Trematoda: Echinostomatidae) were found in seven species of fish. In ruffe, Gymnocephalus cernuus, malformations of the gill filaments apparently caused by these infections were observed. These malformations were in the form of bifurcations of the filaments at about their mid‐length. At the point where the filaments bifurcate, an Echinochasmus metacercaria was always embedded in the cartilaginous ray of the gill filament. All specimens of the ruffe were found to be infected by these metacercariae, and each ruffe specimen was infected by 30–300 metacercariae. Such a bifurcation was found in all of the ruffe specimens, but, apart from these gill malformations, the metacercariae produced only local changes in the cartilage. In the other six infected fish species, only local signs were observed in the cartilage. Experimental infections of chicks with metacercariae resulted in the finding of the sexual adult (marita) of an unidentified species of Echinochasmus. ITS sequences of the adult and metacercaria corresponded with each other, and also with a cercaria isolated from a gravel snail (Lithoglyphus naticoides), with a 99.5–100% similarity.

Stephanoprora amurensis sp. nov., Echinochasmus milvi Yamaguti, 1939 and E. suifunensis Besprozvannykh, 1991 from the Russian southern Far East and their phylogenetic relationships within the Echinochasmidae Odhner 1910

“…Mature worms of this species, like other echinochasmids in the cluster, had 20 adoral spines. Unfortunately, the authors (Molnár et al ., 2016) did not provide a detailed description of morphological characteristics for cercaria but indicated that ‘the tail was almost as long as the body’. However, based on the figure in the publication, this larval stage had a tail that is characteristic of long-tailed Echinochasmidae cercariae.…”

“…Based on the molecular data of the ITS2 rDNA region, Echinochasmus sp. 2, obtained experimentally by Molnár et al (2016), entered the second cluster together with Stephanoprora. Mature worms of this species, like other echinochasmids in the cluster, had 20 adoral spines.…”

“…At the same time, the cercaria shown in micrograph differs in a number of morphological features from cercaria in the figure: ventral sucker is smaller than the oral one vs ventral sucker is equal to or larger than the oral one; and a tail typical for short-tailed cercariae vs tail like longtailed cercariae. Thus, the use of data obtained by Molnár et al (2016) violates the objectivity of taxonomy assessment and analysis of phylogenetic relationships of Echinochasmidae to a certain extent. The greatest problems of taxonomy, systematics and phylogeny arise when, during the study of the life cycle of both echinostomatids and other representatives of digeneans, some developmental stages were obtained experimentally, while others were collected by dissecting naturally infected animals.…”

“…Thus, the use of data obtained by Molnár et al . (2016) violates the objectivity of taxonomy assessment and analysis of phylogenetic relationships of Echinochasmidae to a certain extent. The greatest problems of taxonomy, systematics and phylogeny arise when, during the study of the life cycle of both echinostomatids and other representatives of digeneans, some developmental stages were obtained experimentally, while others were collected by dissecting naturally infected animals.…”